1. Field of the Invention
The present invention relates to a method of forming a positive resist pattern in the process of manufacture of semiconductors.
2. Description of the Prior Art
A positive resist pattern is generally formed according to the following manner. Firstly a positive resist is coated on a substrate such as a silicon wafer to form a resist film, then the resist film is irradiated with an active ray such as a light beam or an X ray through a mask or otherwise irradiated with a scanning active ray such as an electron beam or an ion beam, followed by an alkali development by taking advantage of an increase in solubility of the irradiated portion in an alkali, so as to remove only the irradiated portion and give a final pattern.
This known method of forming a resist pattern may cause occurrence of a surface inhibition layer of the resist film, which may adversely affect the resolution of the resist. In a positive resist comprising a quinone diazide type photosensitizer and a novolak resin, for example, when the resist film is thin or the substrate has a high reflection factor and particularly when a post-exposure bake is accompanied, the surface inhibition layer decreases the resolution. In a chemically amplified positive resist using a photo acid precursor, amine existing in the air deactivates the acid and forms the surface inhibition layer. As is well known, this results in decreasing the resolution, varying the performance of the resist remarkably depending on the time period between the exposure and the post-exposure bake, which is generally referred to as the time-delay effect, and causing a T-shaped profile in which only the surface portion is spread out.
Defects in the pattern after alkali development also sometimes occur. It is generally considered that such defective development is caused by air bubbles produced when a developer is applied onto the resist film and by micro-bubbles due to the gas dissolved in the developer. It is said that the smaller contact angle of the developer on the surface of the resist leads to the less defects of development (the Proceedings of the 43rd Applied Physics Joint Conference, 1996 Spring-Term, 27p-ZW-7 and 27p-ZW-9).